Talspeak system

While the Talspeak system allows the best separation of the group, systems using TBP or TLAHNO- allow good separation of americium with light rare earths whicn, as is well known, make up the bulk of the mass of lanthanides present in the irradiated targets (14). 

An initial experiment involving the treatment of small irradiated Pu/Al targets for the production of americium 243 and curium 244 was carried out in France in 1968 (2). The chemical process was based essentially on the use of a system comparable to the Talspeak system. After plutonium extraction by a 0.08 M trilaurylammonium nitrate solution in dodecane containing 3 vol % 2-octanol, the actinides (americium, curium) were coextracted with a fraction of the lanthanides by a 0.25 M HDEHP -dodecane solvent from an aqueous solution previously neutralized by A1(N0 ) x(0H)x and adjusted to 0.04 M DTPA. The actinides were selectively stripped by placing the organic phase in contact with an aqueous solution of the composition 3 M LiN0 -0.05 M DTPA. While this experiment achieved the recovery of 150 mg of americium 243 and 15 mg of curium 244 with good yields, the process presented a drawback due to the slow extraction of Al(III) which saturates the HDEHP. This process was therefore abandoned. 

Nilsson, M. and K.L. Nash. 2009. Trans-lanthanide extraction studies in the TALSPEAK system Investigating the effect of acidity and temperature. Solvent Extraction and Ion Exchange 27(3) 354-377. 

Collins, E.D., Benker, D.E., Bailey, P.D., Felker, L.K., Taylor, R.D., Delcul, G.D., Spencer, B.B., Bond, W.D., Campbell, D.O. 2005. Hot test evaluation of the reverse TALSPEAK process. Global 2005 Nuclear Energy System for Future Generation and Global Sustainability, October, Tsukuba, Japan. 

The separation of transplutonium elements from the lanthanides constitutes the delicate phase of chemical treatment, owing to their comparable affinities for the usual extractants HDEHP, TBP and TLAHNO3. Among all the systems described in the literature and covered by a recently published critical compilation (JO), we selected those which appeared to be much suitable for adaptation to extraction chromatography the Talspeak process (7) and the... 

Since HDEHP is both a cation exchanger and a coordinator in most extraction situations, coordinated water must be removed from the metal ion in the extraction. Because this sometimes leads to a slow reaction step, the kinetics of HDEHP extraction is important. The kinetics of the Talspeak process (14,15) has been investigated (63) the kinetics of Am(III) and Th(IV) extraction by HDEHP in an unstirred system has also been studied (64). 

Alkyl pyrocatechol extractants provide greater group separation factors. Eu/Am separation factors of 70 have been reported for a non-equilibrium extraction in the system 4-(a,(z-dioctylethyl)-pyrocatechol/NaOH/DTPA (diethylenetriamine-N, N, N, N, N-pentaacetic acid) (or DTPP - diethylenetriamine-N, N, N, N", N"-pentameth-ylenephosphonic acid) (Karalova et al. 1982). The separation factors are based mainly on the difference in the rates of the metal-DTPA (or DTPP) complexation equilibria for Eu and Am. They are therefore highly dependent on the contact time. A principal limitation of the practical application of such a separation scheme is the relatively long contact times (> 10 min) required for extraction. However, the slow equilibration compares favorably with that for other lanthanide-actinide separation processes (e.g. TALSPEAK, section 7). 

Fig. 3. Distribution ratios for trivalent lanthanides and actinides for the TALSPEAK separation system (0.3 M HDEHP/diisopropylbenzene/l.OM lactic acid-0.05 M DTPA-pH 3.0), from Weaver and Kappelmann (1968).

Investigation of the details of this system indicate that at low metal-ion loading the extractant dependence from (1 M lactic acid-0.05 M DTPA) is lowered to 2.1-2.9, dependent on the metal ion. Concentration isotherms for the extraction of lanthanum from lactic acid solutions, with and without DTPA present, indicate that saturation occurs at 1.5 equivalents of lanthanum per mol of extractant monomer, interpreted by the authors as indicative of the extraction of one mol of lactate per extracted metal ion. This observation is supported by actual measurement of extracted lactate concentration. Lactic acid is not extracted by HDEHP in the absence of lanthanum. This separation process has acquired the acronym TALSPEAK (trivalent-actinide/lanthan-ide separation by phosphorus reagent extraction from aqueous komplexes). The generic applicability of the concept is demonstrated by the work of Baybarz (1965), who finds only slightly reduced efficiency upon substitution of 2-ethyl(hexyl)phenylphos-phonic-acid/diethyl benzene for HDEHP/DIPB. 

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